1. Field of the Invention
The present invention relates generally to an in-line filter device adapted to be connected to a compressed air line, and more particularly to such a compact in-line filter device having excellent efficiency of removal of liquid particles such as water and oil vapor contained in compressed air.
2. Discussion of the Prior Art
Generally, a conduit for supplying compressed air to various pneumatically operated components used in factories and atomic plants and for medical applications, for example, is provided with an in-line filter device for removing water and oil vapor from the compressed air flowing through the conduit, in order to protect the pneumatic components.
Various types of such in-line filter devices have been proposed. For example, U.S. Pat. No. 4,487,618 discloses an in-line filter device (airline vapor trap) capable of removing water and/or oil vapor from a compressed airline, with particularly high efficiency.
More specifically described, the airline vapor trap disclosed in the above-identified document includes a first filter having a first pad or packing of wire mesh fibers such as stainless steel fibers, a second filter having a second pad of an absorbent plug structure comprising cotton fabric, for example, and a hollow base which defines an enclosed volume connecting the first and second filters and which is provided with a drain opening. Vapor or liquid particles contained in incoming compressed air are coalesced into droplets while the compressed air is passed through the first filter, and the droplets are trapped within the enclosed volume of the hollow base. The trapped droplets are discharged through the drain opening. Thus, the vapor or liquid particles are separated from the compressed air. As the compressed air stream thus dried is passed through the second filter, any remaining vapor is vaporized. In this manner, water and oil vapor, and dust are efficiently removed by the in-line vapor trap.
For preventing condensation (liquefaction) of a small volume of remaining vapor which has been vaporized, it is desirable to locate the in-line filter device at a point along the compressed air conduit, which is close to a pneumatic component connected to the conduit. However, the in-line filter device of the type described above tends to be comparatively large-sized, due to laterally spaced-apart arrangement of the first and second filters in the form of two independent cartridges apart from each other in the direction of length of the airline conduit. Accordingly, the filter device requires a relatively large space for installation, and therefore there exists a limitation in the location of the filter device selectable along the length of the conduit. In other words, it is preferred to construct an in-line filter device as compact as possible. In this sense, there remains room for improvement in the construction of an in-line filter device of the type as disclosed in the above-identified document.
Further, the filter device shown in the document has another inconvenience. Namely, the filter assembly consisting of the laterally spaced-apart first and second filters is mounted and clamped between an upper cap in the form of a manifold and a lower cap in the form of the hollow base connecting the two filters. The clamping is accomplished by a plurality of fastening members such as bolts extending between the upper and lower caps. When it becomes necessary to replace the filter cartridges, the fastening members must be removed and re-tightened. However, it is difficult to clamp the filter assembly with even tightening forces applied to the fastening members. Uneven tightening forces will cause a potential leakage of the compressed air at the points of connection between the filter assembly and the upper and lower caps.